In recent years the increasing use of therapies involving both acute and chronic contact of materials and blood have brought a keen awareness of biomaterial induced morbidity and mortality. Our understanding of contributory factors to such pathophysiological changes involving alterations to various biochemical systems remains imperfect. It is proposed to investigate specifically the role of leukocytes and postulate that leukocyte involvement is a significant factor in the acute and chronic reactions to an artificial surface in contact with blood. Specifically we hypothesize that (a) studying the interactions of leukocytes with cellular elements will broaden our understanding of thrombus formation on biomaterials and (b) induction of complement activation and impairment of leukocyte function consequent to material contact has major implications for subsequent inflammation responses as well as device related infections. Leukocyte responses to artificial surfaces are complex and varied and include adhesion, aggregation, granule release, expression of cell surface markers and procoagulant activity, fibrinolysis and phagocytosis. It is proposed to investigate these responses using a combination of novel and well-established techniques on a series of well-characterized materials. Polyethylene, silicone rubber, glass and a polyurethane will be used as the test surfaces in all studies. Modified polyurethanes with specific properties may be selectively introduced to extend the study. To determine the relationship between leukocytes and cellular elements particularly platelets the investigators propose to investigate at a fundamental level, the receptor-ligand pair involved in platelet- leukocyte interactions using blocking peptides, divalent cation depletion and antibodies. Further, the investigators propose to determine if platelet-leukocyte interactions result in CD11/CD18 upregulation, tissue factor upregulation and L selectin down-regulation by quantitative and functional assays. The interactions of leukocytes and the contact and complement system will be evaluated by determining the formation of kallikrein-inhibitor complexes, decreases in kininogen coagulant activity and cleavage of kininogen. Activation of the classical complement pathway will be evaluated by measuring C1-C1 inhibitor complexes, C4d and the final pathway by measuring iC3b and C5b-9. In addition to being involved in the blood contacting response to biomaterial surfaces, leukocyte adhesion and activation are also relevant for the pathogenesis of device related infections, a significant source of mortality. We hypothesize that the chemical properties of an artificial surface may affect leukocyte responses either directly or through the modulation of blood components such as complement or coagulation factors. Concomitantly or subsequently bacteria colonization may be affected. The investigators propose to investigate the complex interactions involving bacteria, leukocytes and biomaterials using video microscopy. It is expected that the proposed study will significantly enhance our understanding of the role of leukocytes in pathophysiological changes induces by biomaterials and will ultimately lead to the design of better materials for clinical use.